THE TIBESTI MASSIF is a giant triangular massif located in southern Libya and northern Chad. It lifts abruptly out of the Sahara Desert and is visually impressive. The massif covers an area of over 38,610 square mile (100,000 square kilometer); over 11,583 square mile (30,000 square kilometer) of this area consists of volcanic rock. The Tibesti Massif is separated from the other Saharan massifs to the east and west by deep basins of sedimentary rock. The highest mountain in the Sahara Desert is part of the Tibesti Massif. It is an extinct volcano, reaching 11,205 foot (3,415 meter) above sea level, called Emi Koussi. It sits in the center of the Tibesti Massif and the crater is 11.8 mile (19 kilometer) wide and 3,937 foot (1,200 meter) deep. Emi Koussi is 1 of several stratovolcanos on Tibesti Massif and is almost perfectly intact, with many fine examples of fumaroles, or vapor vents. Tibesti is only 1 of several massifs in the Sahara Desert. The largest massifs in the Sahara are Tibesti, Hoggar in southern Algeria, and Jebel Marra in western Sudan. These massifs formed in the Mesozoic and Tertiary periods with major uplifting in the Earth’s crust. Their formation continued through the Tertiary period and into the Quaternary period, with massive outpourings of lava and more uplifting. Only 1 of the volcanoes on Tibesti has shown any recent stirrings. The rest are considered extinct.